Run-flat tire and method of making same

ABSTRACT

A run-flat pneumatic tire having an annular structural compression element in the inside surface of the crown thereof, which compression element is stabilized by a multiplicity of closely spaced spoke-like radial elements in the tire sidewalls such that de-pressurized operation of the tire without damage is possible. The compression element is a helix with closely spaced coils wound from a rod of a cross-sectional shape selected from various solid and tubular configurations. Round, square, and rectangular coil cross-sectional configurations are shown as are interlocking convex/concave, tongue/groove arrangements. Methods of installing the helical compression element in the tire as by winding up the helix to reduce its diameter such that it can pass through the beads, or by introducing one end of an end coil of the helix over one of the beads into the interior of the tire and providing a relative rotation to feed the helix into the tire are taught. The compression element can be bonded in place and various means for preloading the installed helix are also disclosed.

This is a division of application Ser. No. 410,583 filed Aug. 23, 1982now U.S. Pat. No. 4,428,411.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to radial run-flat pneumatic tires and, moreparticularly, to a run-flat tire having a structural helical coilcompression element inserted in the inside of the casing of the tire andto a method of making the same.

An area of tire technology which has engaged investigators over theyears is the run-flat pneumatic tire concept. A run-flat pneumatic tireis one designed to support a vehicle for operation even if the tire haspartially or totally lost its inflation pressure. The advantages of sucha tire in safety, convenience, cost, and weight and space saving areobvious. A recent successful development in the art of run-flat tires isthe band-reinforced radial tire invented by one of the inventors in thepresent application, which banded tire is the subject of U.S. Pat. No.4,111,249, granted to Edward G. Markow and assigned to the assignee ofthe present invention. The run-flat tire in that Markow patent, U.S.Pat. No. 4,111,249, is hereby incorporated herein by reference.

A banded run-flat tire is a pneumatic radial tire having a casing with acrown and sidewalls extending from the crown on either side to annularbeads which, in a conventional way, are used to mount the tire in asealed relationship on the rim of a wheel. In the design, the bandelement, which usually is a thin structural ring of high-strength steelor a fiber/epoxy composite, is incorporated circumferentially into thecrown of the tire under the tread thereof. Radial tires, as is wellknown, have one or more plies containing a multiplicity of closelyspaced radial reinforcing cords or wires in the sidewalls of the tirecasing. In the tire disclosed in the abovereferenced patent to Markow,the radial cords or wires function as spoke-like reinforcing elements tostabilize the circumferential band. When the tire is deflated, theradial spoke-like elements and the band stabilized thereby form aload-sustaining structure analogous to an elastic arch. In the design,the band receives vertical, drag, and side loads from the road or groundsurface, and carries those loads in compression and bending; the radialspoke-like elements act as tension members to support the axle. A primefunction, also, of the closely spaced radial elements is to stabilizethe thin band against buckling.

Currently suggested banded tire designs under serious considerationusually call for a band embedded in the crown of the tire underlying thetread. Thus, during the manufacture of the tire, it is required withsuch designs that the band be integrated into the "green" carcass orcasing. During the cure cycle, there has to be an accommodation fortransient molding pressures that may degrade the structural integrity ofthe band. Of course, when the band is embedded in the crown itself ofthe tire, the retrofitting of existing radial tires with a band toderive the advantages thereof becomes economically infeasible.

1. Description of the Prior Art

There is a showing in the prior art by V. Alfredo Roque (U.S. Pat. No.3,734,157) of a vehicle tire having annular wire or rod strengtheningelements contained in a plurality of separate ridges on the innersurface of the tire casing. Lacking radial spoke-like reinforcing wireor cord elements in the tire sidewalls cooperating with an annular band,V. Alfredo Roque does not disclose a true radial run-flat tire, however,the teaching therein of annular reinforcing elements in the insidesurface of the crown of the tire is of interest. Because the annularelements are strengthened by annular rods or wire clusters, they have afairly high degree of rigidity. Thus, they have to be incorporated intothe tire during the construction thereof prior to the forming of thebeads. This consideration applies also to the annular bands taught inthe banded radial run-flat tire disclosed in the previously referencedU.S. Pat. No. 4,111,249 to Markow.

SUMMARY OF THE INVENTION

This invention is a radial run-flat pneumatic tire having a casing withan annular compression element therein underlying the crown andsidewalls extending therefrom on either side to annular beads. Astandard radial tire casing having one or more plies of radial textilecords or metal wires extending from bead to bead can be used for thetire of this invention. In this design, the annular compression elementin the crown of the tire is a helix with closely spaced coils, whichhelix is positioned inside the casing of the tire on the inside surfaceof the tire crown radially inwardly of the tread portion. In operation,the annular compression element cooperates with the radial elements inthe tire sidewalls which act as individual tension spokes to provideload supporting strength such that the compression element is reinforcedthereby. For continuous duty, the compression element preferably isbonded in place in the tire. The compression element is a helix made bywinding a solid or hollow rod of suitable cross-section on a cylinder.Variations in the lateral flexibility of the element can be attained byvarying the size, configuration, or material properties of the axiallyouter coils with respect to the axially inner coils of the helix. Thecompression element can be installed in the tire during the tiremanufacturing process or it can be installed subsequently to retrofitsuitable existing radial tires. Installation of the compression elementinto the tire can be effected by winding up the helix to reduce itsdiameter such that it can be installed through the beads into the tireinterior. Alternately, the end of an end coil of the helix can beseparated from the other coils of the helix and introduced over the beadinto the tire casing and the remaining coils can be fed into the casingby a relative rotation between the tire and the helix.

It is thus a principal object of the invention to provide a helicalcompression element for a radial run-flat pneumatic tire that can beinstalled in the tire without necessitating any changes in conventionalradial tire molding equipment and with only minor changes in plantequipment and manufacturing procedures, and further, to provide acompression element which can be installed readily in conventionalradial tires such that any standard radial tire can be retrofitted suchthat it is puncture resistant and has a run-flat capability.

It is another object of the invention to provide a helix for thecompression element for radial run-flat pneumatic tires, the coils ofwhich helix can be wound from rods and tubes of differentcross-sectional configurations and mechanical properties such that theperformance characteristics of the element can be varied as designed totailor the behaviour of the element to meet various operationalrequirements.

It is a further object of the invention to provide an annularcompression element for radial run-flat pneumatic tires in which it isfeasible to replace or to repair the compression element in the event ofdamage thereto.

Yet another object of the invention is to provide a compression elementfor radial run-flat tires in which the physical properties can be variedin an axial direction across the element to impart a desired performanceresponse in the tire in operation.

Another object of the invention is to integrate characteristics of thecompressive element with the current self sealing coatingsconventionally applied to the inner tire crown area.

A still further object of the invention is to provide an improvedcompression element for run-flat pneumatic tires, which element is ofrugged uncomplicated construction, which permits routine retro-fittingof conventional radial tires to give them a run-flat capability, andwhich is of a requisite strength when stabilized by the radial sidewallelements to permit the tire to be run safely at reasonable speeds for arequired distance in an uninflated condition.

Another object is to provide a compressive element, in which during theinstallation process a bonding agent is used and internal pressure isapplied to effect prestressing of the carcass sidewall, whichprestressing enhances the run flat load carrying ability.

Other objects and advantages will become apparent from a reading of theSpecification and a study of the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings the form which is presently preferred; however, it should beunderstood that the invention is not necessarily limited to the precisearrangements and instrumentalities here shown.

FIG. 1 is a sectional view of an embodiment of a tire of the inventionwhich also shows in fragmentary section a wheel with which the tire isadapted to be used;

FIG. 2 is a perspective view of a helical compression element of a tireof the invention; and

FIGS. 3 to 10 are sectional views of various embodiments of the helicalcompression element of a tire of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Having now more particular reference to the drawings, FIG. 1 illustratesan embodiment of a tire 10 of the invention mounted on a wheel 12 whichmay be of a conventional type having a drop center rim 14 welded to awheel body 16. Tire 10 comprises a carcass or casing 18 having an outerperipheral tread portion 20 in the crown 22 of the casing and sidewalls24 extending from either side of the crown to beads 26 in the insideperipheral portions of the sidewalls. Grooves 28 in any desired patterncan be incised in tread portion 20 of the casing 18. Beads 26, which canbe reinforced with the usual annular cords or wires 30, are adapted toseat in an air-tight relationship in the rim 14 when the tire is mountedon the wheel 12. The sidewalls 24 of the casing are reinforced by theusual known weftless radial plies or elements 32. Further reinforcementof the tire in the crown 22 can be provided by means of the usualannular belt or belts 34. Radial elements 32 and belt 34 can befabricated out of steel wires or suitable textile fibers as is wellknown in the art. When mounted on the wheel 12, tire 10 can be inflatedthrough the usual valve (not shown in the FIGS.) in the rim of thewheel.

It will be recognized that the description to this point could apply tothe usual radial tire. A run-flat capability is imparted to the radialtire by an annular structural helical coil compression element 36 (FIG.2) inserted in the tire on the inside surface 38 of the casing 18radially inwardly of the tread portion 20. Compression element 36preferably is a multiple-coil helix of a high-strength material such asa suitable metal or reinforced plastic or composite. High strength, inthe context of the materials used in the annular compression element, isunderstood to mean materials having a tensile strength in the range ofabout 150 ksi and over.

The compression element 36 can be wound from a rod or tube which canhave a suitable cross-sectional shape so as to impart a desired physicalresponse to various operating conditions. As shown in FIG. 3, the coilsof the helix of the compression element can be circular incross-section, the term "circular" being understood to includeconfigurations such as round or oval, and the like, having aclosed-curved shape as in FIG. 10; or the coils can be square (FIG. 4),or rectangular (FIG. 5) in cross section. As indicated in FIG. 3, if thehelix is wound from a tube, the structure will be hollow. If it isdesired to vary the response of the compression element to verticalloads applied across the width W of the element (FIG. 2), the physicalproperties of the material from which the helix is made can be variedacross the width by annealing or tempering or otherwise treatingspecific portions of the helix to obtain the characteristics desired.For example, the coils in the outer ends of the helix can be madestiffer than the coils intermediate the ends. Instead of varying thephysical properties across the width, the cross-sectional size or shapecan be varied. Thus, as shown in FIG. 6, the coils can be reduced insection from the outer coils transversely inwardly. Of course, shouldthe design requirements so dictate, the transverse properties of theelement can be designed such that the intermediate coils are stifferthan the outer coils. Should a greater "cross-beam" shear resistance inthe compression element be required, interengaged coils can be providedfor the helix.

As shown in FIG. 8, one side 40 of the coils is provided with a tongue42 and the other side 44 with a groove 46, the tongue and grooveextending the length of the helix. When the helix is installed in thetire, the tongue 42 is inserted into the groove 46 to engage the coilsof the helix with one another. Should less crossbeam shear resistance berequired, a lesser interengagement can be provided. Thus, as shown inFIG. 7, one side 48 of the coils is given a convex 50 shape and theother side 52 a concave 54 shape, the convexity and the concavityextending the length of the helix. As with the tongue and groovearrangement, the convexity is engaged into the concavity when the helixis installed in the tire. In addition to providing greater cross-beamshear resistance, the interengaged coils enhance the puncture resistancein the crown area of the tire. Should it be desired to have a crossbeamshear resistance that varies across the width of the helix, various ofthe coils thereof will not be provided with interengaging means suchthat some of the coils of the helix are interengaged and some are not.

In the manufacture of the run-flat tire of the invention, a conventionalradial tire casing is used. The compression element can be installed asan added stage in the course of building the tire or the installationcan be done as a retrofit operation on an existing radial tire.Preparatory to the installation of the compression element, the insidesurface 38 of the tire casing is chemically cleaned using any suitablepre-bonding materials and techniques conventionally employed in theindustry. The mating surface of the element is treated with any knownprimer suitable for the material from which the element is constructed.A flexible epoxy or a suitable rubber bonding compound, preferably of aroom-temperature curing type, is applied to the mating surfaces ofcasing and the element. Following this step, the element is insertedinto the tire casing and is pressed radially outward against the insidesurface of the casing and the bonding agent joining the element to thecasing is allowed to cure for a period of time appropriate for thebonding agent used. A prestress can be applied during the curing cycleby means of an inflatable inner tube installed to apply a radiallyoutward pressure on the inside diameter of the compression element.Preferably the inner tube is pressurized during the curing cycle to alevel approximately twice the normal operating pressure of the tire.This pressure is maintained until the bonding agent is cured. As isknown, a parting agent such as a PVC film can be used between the insideof the compression element and the outside of the pressurization tube toavoid adhesion between the two. Upon completion of the curing cycle, thepressurization inner tube is removed and the tire is substantially readyfor use.

In the design of the compression element helix, its width W should besuch that it extends from approximately the shoulder region 56 on oneside of the inside surface 38 of the casing to about the shoulder region58 on the other side. In the helix, with coils having thecross-sectional shapes shown in FIGS. 3 to 6, the spacing between coilscan be established as a function of the lateral flexibility desired.Thus, the coils can be in physical contact or a pre-determined space canbe left between the coils. A further tailoring of the lateralflexibility is obtainable by spacing the coils of the helix and having alayer or thickness of rubber or suitable elastomeric plastic interposedbetween the coils (FIG. 9). The free diameter of the helix is madesomewhat larger than the inside of the tire such that a radialcompressive load is produced between the insert and the tire. Thispreload tends to straighten the sidewalls of the tire; however, arecognized advantage of this technique of prestressing the helix is thatthe stresses thereon in the footprint area of the tire during operationare appreciably lowered. Further, in tires provided with annular belting34, the preload applied by the helix against the crown of the tireplaces the belting into tension to improve its performance.

The compression element helix has a free diameter D (FIG. 2) greaterthan the diameter of the casing inside the tire under the crown anddiameter D is, of course, significantly larger than the inside diameterof the beads over which the helix has to be passed when it is insertedinto the tire. Two methods for overcoming the problem of inserting thehelix through the smaller diameter beads are taught in this invention.In the first method, the helix is placed on a suitable cylindricalmandrel or fixture having a diameter smaller than that of the beads andthe end of one of the end coils is clamped or otherwise held against themandrel. The end of the other end coil of the helix is grasped by asuitable tool and a relative rotation between the tool and mandrel isused to wind up the helix in a direction serving to reduce its diameter.When the helix is wound down to a diameter smaller than that of thebeads, the mandrel and helix are inserted through the bead on one sideinto the tire. When properly positioned between the beads, the helix isallowed to unwind to its free diameter and the mandrel and tool areremoved. It will be appreciated, of course, if the inside of the tireand the outside of the helix have not been prepared for bonding, suchwill be done, as described previously, prior to the insertion of thehelix into the tire. After the helix has been inserted it is bonded intothe tire, also as described previously.

In a second method for inserting the compression element helix, one endof an end coil of the helix is grasped with a suitable tool and the endcoil is drawn apart from the other coils. The end of the end coil isintroduced over the bead into the casing. A relative rotation betweenthe helix and the tire is provided to feed the coils of the helix intothe interior of the tire. In this method, the helix and tire have beenprepared for bonding preferably before the helix is fed into the tire.Once the helix is inserted, the subsequent bonding and curing steps areas previously described.

Although it is generally preferred to bond the helix in place in thetire with a bond capable of resisting shear loads created between theinner casing surface and the outside diameter of the helix, for tiresused in applications where they undergo low duty cycles it is feasibleto use a helix that is not bonded in place. To minimize friction thatcan occur between the casing and the helix that would cause a heat buildup in operation, a film or coating of a low coefficient of frictionmaterial can be applied to the inside surface of the casing or on theouter diameter of the helix.

The compression element when installed in a radial tire acts to providea preload that serves to enhance the load carrying ability of the tireby straightening the tire sidewalls. Its major function, however, is toact in conjunction with the radial sidewall plies to thereby create astructure capable of supporting a full load even when the tire isunpressurized. When the tire is pressurized, the helix acts as a suppletensile member that contributes little or no influence on tireperformance. However, when the tire is deflated, the helix is supportedand stabilized by the radial sidewall elements such that the helix actsas a structural flexible-arch compression member which can support theunpressurized tire for operation under load.

Although shown and described in what are believed to be the mostpractical and preferred embodiments, it is apparent that departures fromthe specific methods and designs described and shown will suggestthemselves to those skilled in the art and may be made without departingfrom the spirit and scope of the invention. We, therefore, do not wishto restrict ourselves to the particular constructions described andillustrated, but desire to avail ourselves of all modifications that mayfall within the scope of the appended claims.

What is claimed is:
 1. In a method of making a run-flat pneumatic radialtire having a casing with a tread portion in the crown thereof,sidewalls having therein a multiplicity of substantially radialspoke-like reinforcing elements extending from said crown on either sideto annular bead portions on the inner periphery on each side of saidtire, said beads being adapted to mount said tire on the rim of a wheel,annular belt means in said tire crown radially inwardly of said treadportion, the method of installing a helical compression element intosaid tire in a position against the inside surface of said crown andradially inwardly of said tread portion thereof comprising the stepsof:coating at least the inside surface of said tire crown with a bondingagent; introducing said helical compression element into said tire intoa position against said crown inside surface; applying a radiallyoutwardly directed force on said compression element to prestress it andto cause its coils to have relative movement with respect to one anotherwhereby the circumference of said compression element and said crowninside surface are expanded to greater than their normal diameter at thenormal operation pressure of said tire such that a prestress istransmitted to said belt means; curing said bonding agent to bond saidexpanded compression element to said expanded crown to lock in saidprestress whereby said tensioned annular belt means act as asupplementary structure with said stressed compression element toincrease the load-capability thereof in the run-flat condition of saidtire.
 2. The method of claim 1 in which the introduction of said helicalcompression element includes the steps comprising:holding one end of anend coil of said helix and rotating the other end thereof in a directionto wind it up such that the outside diameter of said helix is reduced toa size that permits it to pass through the annular bead portion of saidtire; inserting said wound helix axially into said tire to a positionintermediate the bead portions thereof; and allowing said helix tounwind such that its original free diameter is restored.
 3. The methodof claim 1 in which the introduction of said helical compression elementincludes the steps comprising:separating the end of an end coil of saidhelix from the other coils thereof; introducing said end of said coilover the bead into the interior of said tire; and providing relativerotation between said tire and said helix to transfer the remainingcoils thereof into said tire to a position intermediate the beadportions thereof.
 4. The method of claim 1 including the steps prior tothe introduction of the compression element helix into the tire ofcleaning the mating surfaces of said helix and said tire, coating saidmating surfaces with a bonding agent and, after said helix has beeninserted into said tire, curing said bonding agent to bond said helixsecurely to the inside surface of said tire casing.
 5. The method ofclaim 1 wherein the outwardly directed radial force is applied by anannular pneumatic inner tube which has been inserted into thecompression element helix and then inflated.
 6. The method of claim 5wherein the annular pneumatic inner tube is inflated to a pressure thatis twice the normal operating pressure of the tire.